I usually go mid as kog, but bot with a tank or support will do. I cannot stress how op kog is early, and even more late game. Kog'maw, is my champion of choice.

the build i gave you is a build i have almost perfected over the last few months. I actually use all attack speed runes, but the runes listed are probably better.

basically get that w up as much as you can and use it in a fight or youre as useless as an a silenced fiddlesticks.

simple stuff. youve got a ton of attack speed and damage, no need to use any spells unless youre backed up to the turret, then you can just pop your ult at some minions for a little bit of damage.

Kog'Maw is SUPER easy to gank. Keep that ghost or else you'll get crushed early game.

dat passive. Dont be afraid to die early as Kog, try to do as much damage as possible and when you die be ready to right click the one with the lowest hp.